Newborn rats are born with "programmable appetites". As a result it is possible to program the rat for a permanently higher or permanently lower caloric intake in later life simply by controlling the amount of food consumed in the first 21 days of life. Upon stabilization of body weight, rats programmed for a higher caloric intake were 139 g heavier than those programmed for a lower caloric intake and their carcasses contained twice as much fat. If humans are born with "programmable appetites" as the results from other studies imply, then our results would be of extreme importance because obesity is caused by excessive caloric intake.